Introduction and Motivation
Motivation behind designing this shutter is speed, accuracy and variability (activation-time). In our optical tweezers we need to center the trap over a DNA-tethered bead, to get the DNA-overstretching geometry right (this affects the force measurement) and make our feedback program run. To center the tether we need to turn the laser intensity (trap) on/off quickly for various time intervals. To do this we used to use AOM (acoustooptic module), because it’s extremely quick (nano second on/off time). But AOM has some inherent oscillation problem which makes it use as a switch, unsuccessful. So I needed something else, (a shutter) which can replace this AOM function and can be controlled through a foot-switch (paddle).
This shutter does it exact and it is fast (activation-time) with an opening time of 4 and closing time of 2 μsec. The shutter runs on a +5 volts voltage. It moves to an on-position with an active voltage (controlled by the toggle foot switch) working against a restore-spring and remains on when the voltage is applied and turns to off when the voltage is removed. This gives a freedom of choice for the duration shutter is active with very simple electronics used to control the speed (activation time.)
In the design the laser passes through an aperture on the only moving part a cylinder. No gears and no electronics in the design make it very simple, stable and accurate, even under the heat produced by a laser beam. The shutter needs no special power supply and can be run on a cell phone charge with an output of roughly 300mA/5V.
Cost and construction time is also important. With this design, a shutter can be prepared under $40 with 10 hours of construction time (10 x 25 (hourly wage of a technician) =$250+40=$290), still better than many commercially available shutter systems with same performance.
Step 1: Design & Construction
There are three major parts of the system.
The components used:
12V DC motor
Wood rotation stage
Spring with torque of .1 N m
Pillar Post Extension, Length=1" from Thorlabs (shutter cylinder)
30mm Cage Plate Optic Mount from Thorlabs
Post-holder, base-plate ext...
1 power jack M&F
1 1/4" mono Panel-Mount Audio Jack M&F
1 Foot Paddle
1 100Ω pot with, 1 220Ω resistor
1 on/off toggle switch
1 box enclosure
some connection wires, solder gun and solder wire
Any power-supply which can provide 300mA at 5V and above. The motor torque is power dependent and the shutter speed is resorting spring's stiffness (torque) dependent. So choose the spring carefully before decide on the power supply. I would recommend a variable power-supply which can be bought easily from any where.